An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A cosmological model based on the theory of → general relativity, which is homogeneous but → anisotropic. There are actually ten dinstinct Bianchi types, classified according to the particular kinds of symmetry they posses.

Luigi Bianchi (1856-1928), Italian mathematician; → cosmological; → model.

An expert or specialist in biology.

Biologist, from → biology + → -ist.

The study of living organisms and their interactions with the non living world.

Biology, from → bio- + → -logy.

A logical system, such as → classical logic, in which every declarative sentence expressing a → proposition has exactly one → truth value, either → true or → false. Bivalent logic is just a sub-set of a more powerful type of logic known as → fuzzy logic. See also → polyvalent logic.

→ bivalent; → logic.

A collection of 109 impressive celestial objects compiled for amateur astronomers. These objects (→ star clusters, → nebulae, → supernova remnants, and → galaxies), selected from the → New General Catalog and the → Index Catalog, are not present in the → Messier catalog.

Named after Patrick Caldwell Moore (1923-2012), English amateur astronomer, who compiled the catalog in 1995; → catalog.

A list or record of items systematically arranged with descriptive details. → Index Catalogue; → Messier catalog; → New General Catalogue.

M.E. cathaloge, cateloge, from M.Fr. catalogue, from L.L. catalogus, from Gk. katalogos "a list, register," from kata "down, completely" + legein "to say, count," → -logy.

Kâtâlog, loan from Fr., as above.

Same as catalog position and → mean catalog place.

→ catalog; → place.

Same as catalog place and → mean catalog place.

→ catalog; → position.

A standard → syllogism that consists of three → categorical propositions in which there are three terms, and each term appears exactly twice. The three terms in a standard categorical syllogism are the → major term, → mino term, and → middle term.

→ categorical; → syllogism.

The science of dating, of ordering time, of arranging in periods, and of determining temporal distances between past events.

Chronology, from Gk. khronos "time" + → -logy.

Gâhšenâsi, from gâh "time" + -šenâsi, → -logy. Gâhrâik, from gâh + rây, ârâ "order, arrangement" stem of ârâstan "to arrange, to set in order, adorn" (Mid.Pers. ârây-, ârâstan "to arrange, adorn," O.Pers. râs- "to be right, straight, true," râsta- "straight, true" (Mod.Pers. râst "straight, true"), râd- "to prepare," Av. râz- "to direct, put in line, set," Av. razan- "order," Gk. oregein "to stretch out," L. regere "to lead straight, guide, rule," p.p. rectus "right, straight," Skt. rji- "to make straight or right, arrange, decorate," PIE base *reg- "move in a straight line") + -ik, → -ics.

The traditional logic in which → sets are sharply defined (→ crisp set) for example, the number of students registered for a course, or the names beginning with P in a given telephone directory. Classical logic also defines relations between sets of → propositions. Consider for example two sets: elephants and mammals, a simple proposition would be the assertion that all elephants are mammals, that is E ⊂ M, where E is the elephant set and M is the mammal set. The classical logic proposition is either true or false. Compare with → fuzzy logic.

→ classical; → logic.

The scientific study of climates. More specifically, the analysis of weather condition trends over a relatively long period of time (past, present or future). Climatology is distinct from meteorology, which is associated with short-term weather system studies.

→ climate; → -logy.

A shoe made of wood.

M.E., of unknown origin.

Katelé, from (Tabari, Gilaki) katelé "wooden shoe," from katel "tree log, tree stump."

A catalog of → open clusters published in 1931.

Named after Per Collinder (1890-1975) the Swedish astronomer who created the catalog; → catalog.

The logarithm with → base 10. It is known also as the → decimal logarithm, decadic logarithm, or Briggsian logarithm, after Henry Briggs, an English mathematician who pioneered its use.

→ common; → logarithm; → decimal.

A cosmological model developped by Roger Penrose and colleagues according which the Universe undergoes repeated cycles of expansion. Each cycle, referred to an aeon, starts from its own "→ big bang" and finally comes to a stage of accelerated expansion which continues indefinitely. There is no stage of contraction (to a "→ big crunch") in this model. Instead, each aeon of the universe, in a sense "forgets" how big it is, both at its big bang and in its very remote future where it becomes physically identical with the big bang of the next aeon, despite there being an infinite scale change involved, on passing from one aeon to the next. This model considers a conformal structure rather than a metric structure. Conformal structure may be viewed as family of metrics that are equivalent to one another via a scale change, which may vary from place to place. Thus, in conformal space-time geometry, there is not a particular metric g_ab, but an equivalence class of metrics where the metrics ğ_ab and g_ab are considered to be equivalent if there is a smooth positive scalar field Ω for which ğ_ab = Ω g_ab (R. Penrose, 2012, The Basic Ideas of Conformal Cyclic Cosmology).

→ conformal; → cyclic; → cosmology.

A plot showing a summary of correlation at different periods of time.

Correlo-, from → correlation; → -gram.

Pertaining or relating to → cosmology.

→ cosmology; → -al.

A term introduced by Einstein into his gravitational → field equations in order to allow a solution corresponding to a → static Universe. The cosmological constant is physically interpreted as due to the → vacuum energy of quantized fields. See also → dark energy.

→ cosmological; → constant.

The impressive discrepancy of about 120 orders of magnitude between the theoretical value of the → cosmological constant and its observed value. → Quantum field theory interprets the cosmological constant as the density of the → vacuum energy. This density can be derived from the maximum energy at which the theory is valid, i.e. the → Planck energy scale (10¹⁸ GeV). The theoretical vacuum → energy density is (10¹⁸ GeV)⁴ = (10²⁷ eV)⁴ = 10¹¹² erg cm^-3. On the other hand, the observed vacuum energy density is estimated to be about (10^-3 eV)⁴ = 10^-8 erg cm^-3. There is, therefore, a discrepancy of about 120 orders of magnitude.

→ cosmological; → constant; → problem.